1. Field of the Invention
The invention relates to a system and technique for compressing video data in order to minimize the required bandwidth for transmission.
2. Background of Related Art
In recent years, various systems have become available for compressing NTSC video. Such systems aim to decrease required storage space and increase bandwidth available for transmission of data.
VCRs employ a standard technique in which a heterodyne process is used to process chrominance information. However, this technique, known as component sampling, has the disadvantage of requiring the separation of video information into luminance and chrominance. This technique also causes substantial degradation of signal quality because it requires reconstruction of the composite signal after it has been separated into components.
Bidirectional cable systems, useful for such applications as video telephony, have an increased need for compressing data to create available bandwidth. The cables extend from a head end to a fiber node. The fiber node converts optical signals to electrical signals and transmits via coaxial cable, the video signals to various locations in the community. Signals sent over the cables are NTSC signals that include video, color, sound, and synchronization. Available bandwidth limits the amount of audio and video information that can be transmitted. Therefore, because of increased usage of the cable systems, it is desirable to compress signals in order to increase the amount of available bandwidth.
Typically, systems have been designed to avoid the problems associated with limited available bandwidth. For example, many systems are point to point connecting individual classrooms in a campus environment, or video teleconference rooms in a corporate environment. Thus, in these systems users in off-site locations cannot be served.
Yet other systems provide local video telephone service to only a small group of users. For example, U.S. Pat. No. 4,847,829 discloses a system in which analog video terminals are connected to a centrally located analog video switch via dedicated coaxial cables in a star configuration. The number of users is limited by the capacity of the video switch. This approach is not economical for serving a mass consumer market because each video terminal requires a dedicated coaxial cable to access the video switch.
U.S. Pat. No. 4,901,367 discloses a coaxial cable network operating at 800 megahertz that is shared by 60 users, each of which is assigned a dedicated 12 megahertz bandwidth. However, given the assigned bandwidths, this number of users is the upper limit for the application.
U.S. Pat. No. 5,489,947 discloses a digital video signal processing system that receives encoded packets of data representing video image information in compressed form. The video image groups are organized in a compressed component format, (e.g., Y,U,V in the ratio 4:2:2) related to the video image compression format in which pairs of color-related components correspond to more than one pixel. In this and similar methods, the system must discern identical pixel content.
U.S. Pat. No. 5,148,292 discloses a video data processing apparatus in which data compression is performed by dividing a picture image into a predetermined number of blocks of pixels. Video data in each block of pixels are compressed by predetermined processing to reduce the amount of video data that needs to be stored in memory. The processing determines if plural blocks consist of the same pixel data, and if so, the pixel data for only one block are stored.
The aforementioned systems and methods are limited in the amount of bandwidth reduction that can be achieved, or in the complexity of the compression devices. Accordingly, there is a need for a system that can sufficiently reduce bandwidth in order to accommodate a large group of users.